Taking the plunge (line)!

R

Roadracer_Al

Joined
Jan 5, 2013
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135
I just ordered hardware to build a 2x72 belt grinder! It will basically be a no-weld, but welded construction.

I'm excited to build it. I already have most of the steel lying around (I'm a hobby machinist & fabricator), and have a 2 hp 110v 3750 RPM motor -- ought not be lacking for power. Turns out that it was MUCH cheaper to build in a jackshaft with a 2:1 reduction than to buy a 1hp 1725 rpm motor.

I did the SFM calcs, and with a 5-step pulley, I can get roughly from 300 sfm to 3000 sfm, which ought to be a useful speed range.

I'd have preferred a 3-phase/VFD setup, but I can always upgrade to that later if I feel I really need it.

I have to admit, I was really shocked at the price of belts. I ordered all AO to start with.
 
You might want to rethink the belts. I find a blaze belt on steel lasts probably 20:1 or better compared to AO. AO is great for handle material.
 
Quality ceramic belts will more than pay for themselves when grinding steel. Save the AO's for wood and micarta... maybe G10... I couldn't say on the G10, I never bothered trying AO belts on it. I don't even stock AO belts or sheets anymore, I do everything with SiC or the various ceramic belts designed for metal.
 
On the next order, I'll step up to ceramics. I have to let the play money fund refill for a while.

I was in Amazon mode, I'll have to look at some knife making sites for appropriate belts.
 
The 3 M 984 F's are hard to beat at any price. I've used them for two years and find that last longer than any other ceramic belts.
 
Good to know, Fred. Thanks for the tip! There are so many variables on belts it's hard to determine what is useful and what is not. Seems like the splice is the first thing to look at.

I do have a couple of questions about belt tension:

I'd like to use gas springs for both the drive belt and abrasive belt tensioning - they have a clean, direct mechanical action that appeals to me. On a number of the no-weld type grinders, I see people using fairly light springs on the tension arm. It seems that a gas spring in the ~20 lb range would probably be roughly equivalent. Does that sound about right?

Also, is there any reference material about abrasive belt tension? Any benefit to running it tighter than looser? Seems that just tight enough so the drive doesn't slip is probably tight enough.
 
If I could jump in; most of the guys I know including myself that have installed gas pistons use 30 lbs. to tension their belts. The piston itself is not very large so it just looks on the weak side. They are not super expensive so you could try 30 lbs and go from there. I found that 20 is too light and 40 is a little excessive.
 
Thank you for your guidance, Larry. Good data points.

The actual pounds on the belt vary by their mounting location. in relation to the wheel & hinge.
 
For a really adjustable setup, use a small pneumatic cylinder and a small pressure adjuster to set the belt tension.

Here is how one member did it very nicely.
http://www.bladeforums.com/forums/showthread.php/927300-Übergrinder

Here are some comments I made in a past thread on building a grinder:
If building a grinder from the ground up:
A removable tooling arm style is the way to go. These are three wheel type grinders ( four with a flat platen). 1.5" or 2" arms and box tubes will be rock solid.
A second tooling socket below the main arm socket (box) for jigs and work arms. This is a really good feature.
A flat platen the rotates so you can use the 4-6" wheel on the top, the flat part, or the 2" wheel on the bottom.
A contact wheel arm for larger wheels. You can make this with a two wheel rotating end so you can quickly switch from a 6" to a 12" (eg) contact wheel .
A small wheel arm for wheels between .5" and 1.5".
A VFD motor of 1.5HP to 2HP. 1HP will work, but larger will be far more useful down the road.
A foot switch and a remote speed pot are super useful and much safer.
Using gas cylinders or pneumatic cylinders for the belt tensioner. Pneumatic cylinders allow quick increases and decreases in tension.
Making the whole assembly so it can flip on its side and be used as a horizontal grinder.
Overbuild everything. 1/4" plate is a minimum, 1/2" isn't too thick for main components.
Weld everything that isn't adjustable.
Paint the whole assembly except sliding components. Powder coating is even better, and really professional looking.
Make a tooling "tree" type stand with sockets for the arms, and pegs for wheels and other things. Making it with a rotating base will allow more tooling in the same space. Put a box on the top for knobs, wrenches, and tools

Other items, like radiused platens and a water cooled platen mounts are great for those doing high end and production work, but not so much needed by the hobby level maker.

A very good second build is a VFD controlled disc grinder. That would be perfect for the 1HPmotor. This is a very simple build and really useful in the shop. Nathan makes superb precision discs. Wayne Coe makes a quick change disk system.
 
Thank you, Stacy, for the hit list of features. Those are all definitely desirable.

The VFD and pneumatic cylinders are quality upgrades after the initial construction: I have to mind the funds at the moment. I really like the pneumatic cylinder idea: that wasn't even on my radar.

I thought I was clever for coming up with radiused platens and counter-rotating wheels on my own, but I guess not smarter than everyone else. :)

Do you have a reference image for the flat platen with different sized wheels? I'm not sure I"m properly picturing how that goes together. Do you mean that the platen is widely adjustable to accommodate different wheels, not just to align to two wheels of the same size? I assume the benefit is quick access to different diameter wheels?

And, yes, I'm definitely a hobby-level knife maker, although I'm a "committed amateur" machinist & fabricator, motorcycles mostly. The grinder will undoubtedly see much more shop use - specifically grinding HSS lathe tools - than knife grinding use.

There are two "shop tools" which I'm excited about -- a universal surface grinder (adjustable in two axes, skew & tilt, useful for lathe tools), and a tube coping jig. The coping jig is a small wheel grinder which is sized to grind tube-sized notches in preparation for welding. It will need to have an on-center V-block, adjustable for angle, and with X/Y sides - one to feed the work, the other to sweep across the abrasive.

Again, thanks for your input!!
 
Look at some of the grinder in a box and EERF plans and diagrams. It is usually a big triangular piece of metal in the plans with some holes at the corners and a curved groove in the center. It has a flat platen with a larger wheel at the top. You can rotate it to use the larger wheel or the smaller wheel, or set it vertical and use the flat platen. Some have a third wheel on the other triangle corner. It is occasionally referred to as a rotary platen, but that can be confused with KMG's rotary platen, which is very different.

One thing that is important on a grinder build is making sure everything is at 90° angles or aligned perfectly. The tracking arm, drive wheel, flat platen, work rests, etc. should all be set up and made as close to perpendicular/parallel as possible.
 
Thanks for the clarification, yes, I understand. I saw a video recently of KMG's rotary platen: very clever, although it seems to have a *very* specific use.

I'm usually pretty good about building stuff square & straight.
 
I have a question... why can't I find a cast iron step pulley? I have never seen one in iron, and can't locate one on the internet, only zinc.

I ask because my zinc step pulleys arrived with dings and dents in the pulley flanges. Not a big deal to straighten, but wouldn't have happened in iron.

I've been making wheels. The first tool post will be a flat platen, so that requires 2 wheels, and the tracking adjustment requires a wheel for a total of 3. The bearings I ordered are .5" I.D. and 1.125" O.D. I have a large bar of 2" aluminum, so I lopped off several 2.25" lengths and drilled a .625" diameter hole through the middle. These were mounted on an internal expanding mandrel, and turned concentric to the axle hole to a diameter of 1.7". Getting the press fit right on the bearings tripped me up. I totally mis-remembered the rule of thumb (I mixed up press fits with bearing fits), and made the bearing pockets too tight. The bearing would go in with the press, but wouldn't turn because the diameter had been compressed! Fun aspect, the bearing pockets were turned with a trepanning tool, not a boring bar, which will only cut from an existing hole, not make a new annular feature on the work. The trepanning tool is basically a form tool, and it'll hog out a chip .25" wide! Even on the slowest power feed, it was slinging hot, blue, smoking chips into the air with an almost musical "ping" each time the chip broke off. Got a couple that landed in my beard and tried to set it on fire! :eek:

An internal expanding mandrel is a pretty nifty tool. There is a tapered central shaft, and a springy collet-like mating part. To utilize it, you slip the mandrel assembly into the work while the expanding part is on the small end. The you drive the expanding part onto the wide end of the taper, and in theory, it wedges tightly inside the work. In practice, I found that this arrangement has a very limited torque capacity, so light cuts are possible, and heavy cuts spin the expanding part on the tapered shaft, causing it to loosen. Here's what one looks like:

Lathe_Mandrel__Expanding_Mandrel.jpg


I also got the turning finished on the drive wheel. It started as a 3.25" O.D. stainless steel drop from my local scrap metal vendor. Then it got a .625" hole drilled in it. A quick check with a snap gauge revealed it to be slightly undersize (better than oversized!) so a quick pass with the boring bar brought it up to .626" which is what my commercial pulleys measured. Then the fun started. I discovered that the expanding mandrel didn't really like working with stainless, presumably because it's harder and the expanding part doesn't "grip" as well. I got to banging pretty hard on the mandrel, and I was worried about damaging it -- a bent mandrel ain't worth a worthless thing. Anyway this is what came out the other end. I still have to tap for a setscrew, and cut the keyway, which is the next challenge -- I don't currently own a keyway broach. I might just buy a single bushing and broach.

DriveWheelStainlessSm.jpg
 
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Just thought I'd share the latest steps on the belt grinder fab.

I got the keyway cut by using the carriage on my lathe like a key slotter. I had to make a boring bar with a hole perpendicular to the bar and grind a short HSS tool designed to be pushed -- it doesn't have the same edges as a normal boring tool.

I also purchased the material (.25" flat mild steel) and sent the files to a vendor to profile the parts. I'm being a little vague until I get photos of the parts, I think y'all will like them!

Should have them in hand by next week!

Nobody had any thoughts on cast iron step pulleys?
 
The Ceramic belts will save you money in the first batch. As James and others said use the A/O belts for handle materials.

Norton Blaze, 3M Cubitron IIs are fine belts. My favorite for the money and these Ceramic belts are as cheap as many O/A belts are made by VSM. Call the folks at www.trugrit.com

There is also a big diff in how well different brand A/O belts work too. I prefer Hermes Belts.
 
Roadracer_Al said:
Just thought I'd share the latest steps on the belt grinder fab.

I got the keyway cut by using the carriage on my lathe like a key slotter. I had to make a boring bar with a hole perpendicular to the bar and grind a short HSS tool designed to be pushed -- it doesn't have the same edges as a normal boring tool.

I also purchased the material (.25" flat mild steel) and sent the files to a vendor to profile the parts. I'm being a little vague until I get photos of the parts, I think y'all will like them!

Should have them in hand by next week!

Nobody had any thoughts on cast iron step pulleys?
Click to expand...

I've used and still do on one belt grinder of mine the old USA made Chicago brand step pulleys that are for Heating/Air and they work fine. They are Aluminum, whats more important than if they are cast Iron or Aluminum, is that they are balanced properly.

If you bought all of those belts from Amazon, you could send some of them back. You want belts designed for grinding Ferrous metals.
 
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